Denver – Bill Clinton has never done anything on a small scale. He served six terms as governor of Arkansas before his two terms as president and now travels the world as head of a foundation that dispenses millions of dollars to fight disease and climate change. On the side, he earns more for one speech than most Americans make in a year.

Now, in a week that is supposed to be all about Barack Obama and his battle for the presidency against John McCain, former President Clinton has carved out an outsize role for himself here in Denver. Even if his wife, Hillary Rodham Clinton, has publicly said all the right things after losing a tough Democratic nomination fight with Senator Obama, Mr. Clinton has not.

And up until the moment he delivers a prime-time convention speech Wednesday – his sixth such address in as many presidential cycles – no one can be quite sure if Clinton’s appearance will help or hurt Obama. The greatest danger may well be that Clinton spends the bulk of the time talking about himself, doing little to convince voters that he and his wife are ready to cede the spotlight to Obama.

“He can do what Mario Cuomo did for him in 1992,” says Jack Pitney, a political scientist at Claremont McKenna College in California, referring to the then-New York governor’s convention speech nominating Clinton. “Everybody was wondering whether it would be a Mario-fest, but Cuomo very wisely kept saying the name Bill Clinton – Bill Clinton is this, Bill Clinton is that. The more that Bill Clinton mentions Barack Obama, the better it will be for the Democratic Party.”

Another risk is that he may get the words right, but in a tone or with body language that betrays a hint of dismay. That will only fuel the story line that the Clintons may not want Obama to win in November, so Mrs. Clinton can try again in four years. Of course, if Obama does lose, and either Clinton is seen as having hurt the Illinois senator’s chances, that could doom Mrs. Clinton’s prospects as a future presidential candidate.

It’s also highly possible that the former president will deliver a pitch-perfect address and take a big step toward winding down the Clinton-Obama soap opera. After all, Clinton is one of the great political showmen of his time. Even when he bombed in his first, overlong convention address – the 1988 nominating speech for then-Gov. Michael Dukakis of Massachusetts – he quickly recovered by appearing on the Tonight Show, where he played the saxophone and made fun of his convention flop.

“Americans saw that Clinton had a sense of humor and that tended to neutralize the damage,” historian Michael Beschloss later said on PBS.

Throughout the 2008 primary season and beyond, Clinton has made no secret of his exasperation with Obama’s success. He called Obama’s anti-Iraq war message a “fairy tale,” and after facing accusations that he had played the “race card” in the run-up to the South Carolina primary, Clinton later accused the Obama campaign of “playing the race card on me.” When asked in a recent ABC-TV interview if Obama was ready to be president, Clinton replied: “You could argue that no one’s ever ready to be president.” Clinton has since steered clear of the media.

Representatives of both camps say that the two men have spoken in the past week and that the conversation went well.

Still, there’s no doubt that the longstanding friction between Obama and both Clintons has emerged as one of the dominant story lines of convention week and is in danger of being overblown. With so many media on hand – 15,000 credentials have been issued – in constant search of stories, the Clintons (and their die-hard supporters) have been an obvious focus. When Obama offered both Clintons prime-time speaking roles and the opportunity to have Senator Clinton’s name placed in nomination, he may have thought that would satisfy the need to honor the Clintons’ status as the party’s premier power couple.

But with the Clintons speaking on separate nights, that generates two days of headlines instead of one. And with Clinton speaking the same night as Sen. Joseph Biden of Delaware, the former president threatens to overshadow Obama’s running mate.

Former Clinton aides have also kept the story line going – both in blind quotes to the press and publicly. Privately, the Clinton camp suggests that Obama has not done enough to help Hillary Clinton retire her campaign debt. Last week, in the New Republic, former Clinton aide Howard Wolfson wrote that “there is still work to do on the Bill Clinton front.

“He feels like the Obama campaign ran against and systematically dismissed his administration’s accomplishments,” Mr. Wolfson continued. “And he feels like he was painted as a racist during the primary process.”

Typically, ex-presidents ascend to a status of elder statesmen, doing good works. Clinton is the first ex-president to get back into the rough and tumble of the political game on behalf of his wife, and the risks have now become self-evident.

But he is not the first young ex-president to be seen as making mischief in his own party after leaving office.